253 
rejecting all mean daily temperatures below 6° C., and thus finds 
1,496° as the mean value of the sum of temperatures from the date of 
sowing to that of flowering. The similar sum from the date of head- 
ing to flowering is 860°, or 1,496° less 639°. 
The fourth epoch, or the ripening of the wheat, occurs when the 
sum total of the mean daily shade temperatures since the date of 
flowering, rejecting all below 6° C., amounts to 815° C., and in the 
climate of Paris this occurs about forty-five or forty-six days after 
the date of flowering. The range of uncertainty in this last interval 
is only four or five days, owing largely to the uniformity of the 
climate at this season. It is the best defined of all the periods and 
so well ascertained that, knowing any actual date of flowering we 
can safely predict the date of ripening. In proportion as we 
approach the latter date the process of ripening seems to concentrate 
itself more and more within the wheat; water and sunlight become 
less and less important; rain becomes a source of uneasiness as to 
the harvest, and the intensity of ‘sunshine has only an indirect 
influence on the quality and quantity of the grain. The influence 
of sunlight during the first phase or germination is negligible and 
probably nothing; it is a maximum at the beginning of the fourth 
phase, but diminishes rapidly as the fourth phase progresses and in 
proportion as the wheat becomes more yellow. We shall therefore 
consider the amount of sunshine, or more properly the total radiation 
from sun and sky, during the first thirty days after flowering and 
neglect its amount during the remainder of the period up to maturity. 
The following table shows the amount of radiation, as expressed 
by Marié-Davy in actinometric degrees or percentages and com- 
puted from actual observations of his actinometer at Montsouris for 
the various stages of growth, viz, the second or heading stage from 
germination to heading, the third or flowering stage from heading 
to flowering, and fourth for the first thirty days of the fourth or 
ripening stage immediately following the flowering: 
Total radiation received 
Total radiation received | Total radiation received during 30 days of ripen- 
Year of sow- during heading stage. during flowering stage. ing stage 
ing. ‘ 
a. b. Cc. d. i, {| i. | C. | d, Gi) bs C. | d. 
I Gis See ee 842 | 1,332 | 1,755 | 1,848 | 3,205 | 2,979 | 2,870 | 2,954 | 1,176 | 1,608 | 1,548 | 1,581 
ik k a A See 908 | 1,191 | 1,663 | 1,938 | 3,031 | 2,983 | 2,620 | 2,482 | 1,403 | 1,220) 1,171 | 1,194 
Gay. 32 = eens 904 | 1,009 | 1,161 | 1,247 | 3,214 | 3,169 | 3,169 | 2,821 | 1,419 | 1,504 | 1,526 | 1,558 
ioe 6525 | 608ciemo461l A SLT ee sb ashee eae Es Remar) pe veal [a Al bf cae | a \weewete’: 
1G 5 733 739 977 | 1,255 | 2,096 | 2,302 | 2,282 | 2,208 | 1,103 | 1,199 | 1,399 | 1,450 
iD 2 seus 800 | 1,382 | 1,476 | 1,743 | 2,749 | 2,634 | 2,630 |.2,506 | 1,320 | 1,496 | 1,131 1,184 
TS es Seen 840 | 1,251 | 1,582 | 1,600 | 3,095 2,580 | 2,658 | 2,607 | 1,076 | 1,092 | 1,321 | 1,362 
ic) 1,000 | 1,578 | 1,924 | 1,991 | 3,519 | 3,106 | 2,849 | 2,865 | 1,391 | 1,433 | 1,493 | 1,486 
Average of | | | | | | | 
6 years-.-_- 857 | 1,117 | 1,497 | 1,653 | 2,977 | 2,808 | 2,728 | 2,629 | 1,268 | 1,363 | 1,360 | 1, 363 
